Dies for thread rolling machines for producing screws



June 22, 1965 F. w. COOPER ETAL 3,190,095

DIES FOR THREAD ROLLING MACHINES FOR PRODUCING SCREWS Filed Oct. 10,1962 2 Sheet s-Sheet 1 mvnvro a reform: M LL/an Coo Pit 15M! F025 y T)!June 22, 1965 F. w. COOPER ETAL 3,190,095

DIES FOR THREAD ROLLING MACHINES FOR PRODUCING SCREWS Filed Oct. 10,1962 2 Sheets-Sheet 2 Mil/Enron.

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United States Patent r 3,190,095 DIES FOR THREAD ROLLING MACHINES FURPRODUCING SCREWS 7 Frederick William Cooper, Birmingham, andJohn'Forsyth, Longdon, near Rugeiey, England, assignor's 'to G.K.N.Screws & Fastener Limited, a British company Filed Oct. 10, 1962, Ser.No. 229,582 Claims priority, application Great Britain, Oct; 14-, 1961,36,957/ 61* 2 Claims. (CI. 72-88) This invention relates to. dies usedfor-the production of certain types of screws, by thread rolling whereina blank is rolled between co-operating dies,'the dies having rib andgroove formations to produce the desired thread form on the blank. I tThe expression screws as used herein is to be considered in the genericsense as including drive nails, and the like, which have a spaced-threadform as defined hereinafter.

Certain screws, such as machine screws, have relatively sharp threads offine pitch such that the die form for producing them by threadrollingconsists. of sharp ribs and sharp (generally V section) grooves but thetype of screws with which this invention isconcerned are those which arereferred to in this specification as spaced-thread type and in which theconvolutions of the thread are spaced apart by grooves, which may beflat bottomed, rounded, of generallyU form, or otherwise non-sharp, suchthat the corresponding die form,-in the thread roiling operation, needsribs of fiat top, rounded, or other non-sharp form to produce thesegrooves.

Considering the type of machine which has a pair of flat dies which arereciprocated relatively to roll the blank therebetween, the form of theflat die used hitherto for producing spaced-thread screws has been suchthat the crosssection of the die changes in form between the startingend and the finishing end. Over the finishing end of the die the threadform thereon has grooves to produce the desired thread ribs on theblank, and flat top or other non sharp ribs to produce the desiredgrooves on the blank, but at the starting end of the die the ribs havehad to be made sharp in order to obtain an initial deformation of themetal of the blankunder relatively low pressure. The sharp form of theribs gradually flattens out along the length of the die until it mergesinto the flat top or other non-sharp form at the finishing end.

Also, to prevent skidding of the blankwhen it first enters between thedies it has heretofore been necessary to roughen the surfaces of thedies at the starting ends and this has usually been done by providingtransverse serra-' tions. These serrations, although consideredessential, are a drawback because they'interrupt the thread form on thedie and can produce undesirable flaws in the finished thread on theblank.

The object of the invention is to provide improvements in the dies usedfor producing these spaced-thread type of screws by a thread rollingoperation. According to the invention I provide a die for use inproducing a spaced thread type of screw wherein at the finishing end ofthe die the cross-sectional form is such as to provide ribs havingcrests which are of the desired flat top, rounded, or other non-sharpform and at the starting end of the die the cross-section provides ribswhich are somewhat similar in section to' those at the finishing end buteach rib at the starting end has its crest interrupted to provide thedesired degree of sharpness, the interruption decreasing along thelength of the rib from the starting end to the finishing end of the die.

. The interruption of the crest of each rib may be in the form of agroove or grooves of relatively shallow depth and the or each groovewould be formed so that it deice creases in depth as it progresses fromthestarting end of the die until it disappears completely at theposition where the rib merges into the finishing end of thedie;

The invention is illustrated in the accompanying-draw ings wherein:FIGURES lA and 1B are given as examples to'show the form of thread onspaced-thread type screws. H

FIGURE 2 is a diagrammatic illustration of a 'diejaccording to theinvention for use in a flat die type of threadrolling machine. I it iFIGURE 3 shows three fragmentary views showing" the cross-section of thedie form on the three lines A"A; V

BB,'D-D, in FIGURE 2. 1 FIGURE 4 shows three alternatives for thecross-sectional die form on the line AA of FIGURE 2. 1 f} The spacedthread types of screws illustrated in FIG URES 1A and 1B eachhave threadconvolutions 10 which are spaced apart by grooves 11- having flat, orsubstanf tially fiat bottoms. r p {j Inthe production of a self-tappingscrew whichhas a relatively sharp thread form, such as that shown inFIG- URE 1A, the form of the die 12 for producing sucha screw is suchthat over the finishing section 13, theicrosssection (see DD in FIGURE3) providesribs 14 spaced apart by relatively deep grooves. 15 which aresuch as to form the actual thread lfl'while the ribs 14 haveflat tops 16and outwardly converging side faces 17 to-produce the fiat bottomgrooves 11 betweenthe convolutions of the thread It I At the startingend 18 of the die the cross-section '(see A-A in FIGURE 3) is somewhatsimilar to that at" the finishing end (section D- D) except that theflattop of each rib 14 is interrupted by a relatively shallow groove 19which may be of part-circular section and which-in elfect produces tworidges 20 at the top of the rib thus creating a degree of sharpness andthis groove 19 continues along the length of each rib but graduallydecreasing in depth (see section B--B) until it disappears completely atthe position where the rib runs into the finishing section 13 of thedie.

The groove 19 may take various forms depending upon the degree ofsharpness required, the nature of the material of the blank and thedimensions thereof, and instead of one groove there may. be two or moregrooves. Certain alternatives for the form of the groove 19 or groovesare shown in FIGURE 4. In the top'view the groove 19 is of sharp V formbut shallow as compared with the depth of the thread forming grooves 15.

In the view next below there are two quite shallow grooves 19a along thetop of each rib separated by a fairly shallow ridge while in the bottomview there are two grooves 19b of more pronounced depth separated by apronounced rib but of shallow depth as compared with the thread forminggrooves 15. Such grooves 19, 19a, 1%, as shown in FIGURE 4 graduallydecrease in depth along the length of each rib until merging into thefinishing section of the die, as described'above in connection withFIGURE 3.

. One advantage of dies made in accordance with the invention asoutlined above is that the provision of serrations or other form ofroughening at the starting end 18 of each die can be eliminated or verysubstantially reduced as it is found that there is considerably lessdanger of skidding.

of the blank when first introduced between'dies which have been formedin accordance with the invention. Consequently better threads can beproduced on screws as the danger of flaws being produced issubstantially reduced or eliminated.

Further it has been observed in practice that the thread form producedon the screw is generally better than that produced by dies usedhitherto and it is considered that the presence of the interruption (thegroove 19 or grooves) in the crestsof the ribs 14 at the starting end ofthe die in some manner givesa better control over the flow of the metalof the'blank and appears to provide a more progressive gathering anddisposing of the metal than does the conventional die as used hitherto.This has been observed particularly, in connection I with self-tappingscrews Where hitherto the grooves, between theconvolutions of the threadare not truly flat but have slight con cavity, whereas, withdies inaccordance with the invention, a more true flatbottomed grooveisobtained thus indicatingthat there has'been a more faithful followingof the contour at the finishing end of thei'die by themetal of the blankas it is flowing under, pressure. V

In applying the invention t'o-a machine having a pair of flat dies oneof which may be fixed while the other reciprocates, the invention ispreferably applied to both dies. However, if greater economy is desired,the one die can be'con'structed in accordance with the invention whilethe other die may be formed so that it has a constant cross-sectionalform from end to end, this .form being the same as at the starting endof the die which is in accordance with the invention (i.e. section A-A),with the aforesaid interruptions or grooves 19 being continued-at thesame depth thronghoutthelengths of the ribs from end to end of the saidother die. Withthis arrangement thisilatter'die being .of constantcross-sectional form, can bereversed end for end when any substantialwear has taken place along one side of the die so as to make moreeconomic use of the whole 'of the die face. With such an arrangement thefinishing end of the one. die which has the hat top ribs and isconstructed in accordance with the invention is theme which dictates thefinal form of the thread.

Also, although the invention, has been particularly def scribedinrrelation to flat dies, it may also be applied to machines:wherein-the blank is rolled between two or thread form 'on itscircumference.

a a 4 What we claim then is:

[1. A die for use in rolling a thread upon .a blank to produce a spacedthread type of screwhaving; onits blank engaging face, a thread formcomprising alternate,

ribs and main grooves extending from the1 startingend to the finishingend of the die and wherein, at the finishing end of the die each rib hasa crest which is, of flat-top form and, at the starting end of the die,each rib hasca' form which is" similar to that at theyfinishingfiendybuteach rib at the starting end having'its crest provided with atleast one1 groove, extendingflongitudinally of the rib and of a depth which isrelatively, shallow as compared i, with the depth of the main grooves,such groove decreasing in depth fromthe starting endto the finishing endof each-rib until itdisappears at ,a position short of the finishing endof eae'hrib; Y

2. A pair ofidies for use in a flat die rolling machine; I

in which the dies are reciprocated relativelyl toone another, whereinone die is'constructed in accordance with claim 4, the other die havingon its blank engagingface; a thread form comprising alternateribs andmaingrooves,

, extending from the starting end to the finishing end ofjthe die, andwherein each rib ofsuch die has "a' form which is the same as the formof a rib at the starting end of the first mentioned die,,with th'e'cresto'f each rib provided with at least one groove extendinglongitndinally'of the rib and of a depthrwhich is-relatively shallow ascompared with the depth of the main grooves.

' References Cited by the Examiner, "UNITED STATES PATENTS 7 2,391,30812/45 Hanneman nusi s0 9 WILLIAM J. STEPHENSON; Primary Examiner.

CHARLES LANHAM, Examiner. I

1. A DIE FOR USE IN ROLLING A THREAD UPON A BLANK TO PRODUCE A SPACEDTHREAD TYPE OF SCREW HAVING, ON ITS BLANK ENGAGING FACE, A THREAD FORMCOMPRISING ALTERNATE RIBS AND MAIN GROOVES EXTENDING FROM THE STARTINGEND TO THE FINISHING END OF THE DIE AND WHEREIN, AT THE FINISHING END OFTHE DIE EACH RIB HAS A CREST WHICH IS OF FLAT-TOP FORM AND, AT THESTARTING END OF THE DIE, EACH RIB HAS A FORM WHICH IS SIMILAR TO THAT ATTHE FINISHING END, BUT EACH RIB AT THE STARTING END HAVING ITS CRESTPROVIDED WITH AT LEAST ONE GROOVE, EXTENDING LONGITUDINAL OF THE RIB ANDOF A DEPTH WHICH IS RELATIVELY SHALLOW AS COMPARED WITH THE DEPTH OF THEMAIN GROOVES, SUCH GROOVE DECREASING IN DEPTH FROM THE STARTING END TOTHE FINISHING END OF EACH RIB UNTIL IT DISAPPEARS AT A POSITION SHORT OFTHE FINISHING END OF EACH RIB.